SOUTH KOREA (Next Animation Studio) – The Galaxy Note 7 is probably Samsung’s most famous model, not for its design or specs, but for its notorious tendency to spontaneously combust. After two recalls that cost the brand at least US$5 billion, the South Korean phone giant has finally revealed where exactly it all went wrong.

The findings were detailed in a press conference held in Seoul, South Korea by Samsung mobile chief DJ Koh. According to Koh, the batteries were the culprit. Both the original and replacement batteries had manufacturing defects. And though the root causes were different in each case, the results were the same, reports Forbes.

The Galaxy Note 7 was fitted with 3500 mah lithium ion batteries, which should have enough space to allow negative electrodes to remain straight. However, those manufactured by company subsidiary Samsung SDI were found to have deflected negative electrodes, which caused the batteries to overheat and explode.

As a result, Samsung recalled and reissued all Galaxy Note 7 phones in September.

Replacement batteries were made by Hong-Kong based affiliate Amperex Technology, but were likewise defective. Welding burrs penetrated through the separator and insulation tape, causing negative electrodes to be in direct contact with the positive tab.

In some cases, batteries were missing the insulation tape altogether. According to the subsequent investigation, both factors were linked to the phone overheating and potentially catching fire.

Samsung ultimately cancelled production of the smartphone model, and has had to re-assess existing safety measures.

Business Insider reports that along with the battery findings, the company has announced the implementation of a new 8-point battery safety check that’s meant to reassure consumers that safety is now top priority.